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Magnetic circular dichroism (MCD) spectroscopy is a source of important data about the electronic structure and optical properties of different chemical systems. Theoretical simulation of the MCD spectra can be used to assist in the understanding of empirically measured MCD spectra. In the present paper, a theoretical investigation of electronic and optical properties of phosphine-protected gold clusters with a Au93+ core with D2h symmetry was performed with time-dependent density functional theory. The influence of ligands on the optical properties of the gold core was investigated. Simulations of the optical absorption and MCD spectra were performed for the bare gold Au93+ cluster as well as for ligand-protected Au9(PH3)83+ and Au9(PPh3)83+ species. MCD spectra were calculated at a temperature of 298 K and a magnetic field of 7 T. A comparative analysis of theoretical and experimental data was also performed. The obtained results show that the theoretically simulated MCD spectrum for the Au9(PPh3)83+ ion in gas phase exhibits a reasonable agreement with experimental results for the [Au9(PPh3)8](NO3)3 system, although with a red shift of up to 0.5 μm-1. Overall, MCD provides significant additional details about the electronic structure of the considered systems compared to the absorption spectra. [ABSTRACT FROM AUTHOR]

The equilibrium geometries of four asymmetric spirosilabifluorene derivatives are optimized by means of the DFT/B3LYP method with the 6-31G basis sets in this paper. On the basis of the optimized structures, the electronic structure and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) based on the 6-31G level combined with the sum-over-states (SOS) method. The results show that these compounds possess remarkably larger molecular second-order polarizabilities than typical organometallic and organic compounds, and replacement of a carbon atom with nitrogen within the conjugated substituent has a great influence on the second-order nonlinear optical properties. Analysis of the main contributions to the second-order polarizability suggests that charge transfer from the z-axis directions plays a key role in the nonlinear optical response. These compounds have a possibility to be excellent second-order nonlinear optical (NLO) materials from the standpoint of large values, small dipole moment, high transparency, and small dispersion behaviors. [ABSTRACT FROM AUTHOR]